<template>
    <ul class="list">
        <li class="item" v-for="item of letters" :key="item" :ref='item'
        @click="handleLetterClick"
        @touchstart.prevent = 'handleTouchStart'
        @touchmove = 'handleTouchMove'
        @touchend = 'handleTouchEnd'
        >{{item}}</li>
    </ul>
</template>
<script>
export default {
    name: 'CityAlphabet',
    props: {
    cities : Object
    },
    data() {
        return {
            touchstatus: false,
            startY: 0,
            timer: null
        }
    },
    updated() {
        this.startY = this.$refs['A'][0].offsetTop
    },
    computed: {
        letters(){
            const letters = []
            for(let i in this.cities){
                letters.push(i)
            }
            return letters
        }
    },
    methods: {
        handleLetterClick(e) {
            this.$emit('change',e.target.innerText)
        },
        handleTouchStart() {
            this.touchstatus = true
        },
        handleTouchMove(e) {
            if(this.touchstatus){
                if(this.timer){
                    clearTimeout(this.timer)
                }
                this.timer = setTimeout( () => {
                const touchY = e.targetTouches[0].clientY - 79
                const index = Math.floor((touchY - this.startY) / 20)
                if(index >= 0 && index < this.letters.length){
                this.$emit('change',this.letters[index])
                }
                },10)
                

            }
        },
        handleTouchEnd() {
            this.touchstatus = false
        }
    },
}
</script>

<style lang="stylus" scoped>
@import '~styles/varibles.styl';
.list
    position absolute
    top 1.58rem
    right 0
    bottom 0
    width 0.4rem
    display flex
    flex-direction column
    justify-content center
    .item
        text-align center
        line-height .4rem
        color $bgColor
     
</style>